research shows that different forms of TSEs occur in different animals, each with slightly different characteristics to the other forms (e.g. BSE in cattle, Scrapie in sheep, CJD in humans). These different forms are referred to as strains. It is thought that the different strains are caused by slight differences in the glycan structure around the PrPc found in the various species that are affected by TSEs.

Different forms of the sheep TSE scrapie have been isolated by transmission to mice. These strains cause variations in the incubation period and pattern of pathology observed in the infected animal. As yet no strains of CJD have been identified.

Different forms of the scrapie have been isolated by transmission to mice. These strains show distinct variations in the incubation period and pattern of pathology observed in the infected mice.

a strain is an overstretching of a ligament or muscles caused by overexertion. (In this case there is no actual tear.)

a diverse pool of viruses among aquatic wild bird populations, the avian influenza (AI) viruses

a negative prognostic factor

a top priority from both a medical and an economic viewpoint